JPA and Hibernate -- Manual Flush

[Greg Charles]

I've read in several places, including "Seam in Action" (Manning), that an important part of Hibernate not supported by JPA is manual flush. However, the JPA EntityManager does have a flush() method, so I'm a bit confused. Does it mean that JPA allows manual flushes, but you can't stop it from also auto-syncing to the database as it sees fit? Or does it mean that em.flush() won't have any effect unless using the Hibernate implementation of JPA?